A power supply voltage monitoring circuit outputs a power supply voltage monitoring output signal externally when a power supply voltage is, for example, lower than a predetermined voltage. This power supply voltage monitoring output signal is used as an enable signal of, for example, a CPU (Central Processing Unit) or a DSP (Digital Signal Processor).
In the related art, there is provided a power supply monitoring circuit capable of operating at a low power supply voltage without deteriorating detection accuracy of power supply voltage. The power supply monitoring circuit in the related art switches one of an output of a constant-voltage generating means for generating a predetermined voltage reference value and a resistance division value of a power supply voltage, which are input to a comparator that compares the two inputs to a separate reliable predetermined voltage, by using a control means, in a low power supply voltage region in which an operation of the constant-voltage generating means is undetermined, thereby preventing an error in the power supply monitoring output due to undetermined comparator input. Further, in the related art, there is provided a general circuit configuration of the power supply monitoring circuit that compares the power supply voltage with the output of the constant-voltage circuit and outputs a monitoring signal externally when the power supply voltage drops to be less than or equal to the output of the constant-voltage circuit. In the power supply monitoring circuit of the related art, since a power supply voltage of a predetermined value or more is required for the constant-voltage circuit to function normally, the power supply monitoring circuit may not function normally in the low power supply voltage region where the power supply voltage is equal to or less than the predetermined value, and the power supply monitoring output may be erroneously output due to an undetermined voltage reference value, that is, an undetermined input state of the comparator.
In the related art, there is provided a voltage detecting circuit capable of adjusting a hysteresis voltage. In the related art, the voltage detecting circuit includes a first resistor, a second resistor, and a third resistor connected in series between a first power supply and a second power supply, and further includes a voltage dividing circuit that outputs a divided voltage value of a potential difference between the first power supply and the second power supply from an output terminal, which is a connection point between the first resistor and the second resistor. The voltage detecting circuit further includes a reference voltage circuit that generates a reference voltage, and a comparator that receives a signal based on the output of the voltage dividing circuit and the output of the reference voltage circuit and outputs a signal as an output of the voltage detecting circuit. The voltage detecting circuit further includes a switch connected in parallel with the third resistor between the second resistor and the second power supply, and a hysteresis voltage control circuit that receives a signal based on the output of the comparator and outputs a signal for controlling the switch. The hysteresis voltage control circuit outputs a signal to turn on the switch when the output of the comparator is inverted for the first time from a reset state, and outputs a signal to turn on the switch when the output of the comparator is inverted for the second time and thereafter in a state where the switch is turned off. Further, the hysteresis voltage control circuit has an input terminal to which the output of the comparator is input, a reset input terminal to which a reset signal to reset the hysteresis voltage control circuit is input, and an output terminal from which a signal for controlling the switch circuit is output.
In the related art, there is provided a reference voltage generating circuit capable of generating a reference voltage having small dependency on process, variation and temperature change and having small variation, and a power supply device using the same. In the related art, the reference voltage generating circuit has a circuit configuration in which an NMOS depletion transistor as a constant-current source is connected in series with an NMOS transistor having a threshold voltage different from that of the NMOS depletion transistor, and a drain of the NMOS depletion transistor is connected to a power supply voltage, a gate and a source thereof are connected to an output voltage terminal, and a substrate is connected to a GND potential. Further, the drain and the gate of the NMOS transistor are connected to the output voltage terminal, and the source thereof and a substrate are connected to the GND potential. The NMOS depletion transistor has a substrate bias coefficient that gives a change in the threshold voltage so that such a change is substantially equal to a voltage change of the output voltage terminal, and also has the threshold voltage so that it does not become an enhancement type.
In the related art, there is provided a power supply capable of solving a trade-off between suppression of leakage current of an output transistor and reduction in current consumption. In the related art, the power supply includes an output transistor, a power supply circuit that generates an output voltage from a power supply voltage by using the output transistor, and a leakage current absorbing circuit that absorbs a leakage current of the output transistor by using a depletion type transistor. Further, in the related art, there is provided a reference current generating circuit capable of solving a trade-off between reduction in circuit scale and reduction in current consumption. In the related art, the reference current generating circuit includes a reference voltage generator that generates a reference voltage using a depletion type transistor, and a voltage/current converter that generates a reference current from the reference voltage. In the related art, the power supply further includes an internal power supply voltage generating block that generates an internal power supply voltage upon receiving a power supply voltage, a reference voltage generating block that generates a reference voltage upon receiving the internal power supply voltage, and a power supply block that generates an output voltage from the power supply voltage so that a feedback voltage corresponding to the output voltage matches the reference voltage. The internal power supply voltage generating block includes a reference current generating circuit and an internal power supply voltage generating circuit that generates an internal power supply voltage using a reference current.
In the related art, there is provided a power supply voltage monitoring circuit capable of monitoring even a low power supply voltage by eliminating the need for a constant-voltage circuit. In the related art, the power supply voltage monitoring circuit includes a voltage dividing means that divides a power supply voltage, a comparator which receives a divided voltage and a zero voltage and compares the voltages to output a result of the comparison, and an output transistor means that outputs a monitoring signal by the output of the comparator. The comparator has a configuration in which an area ratio is given to a transistor pair constituting an input stage differential amplifier and an offset voltage obtained from the area ratio is compared with a divided voltage.